RE: G-26 ZENOAH, FLAMES OUT
The cowl need not be opened. See post 20. The ring shaped air exit is extremely effective, especially if the incoming air area is restricted to engine front entry only. A ratio of 1:1.2 will be perfect if pressure difference between air intake (ram air) and air exit (suction) is good.
I often get away with a ratio of mere 1:0.8 by forcing all cooling air through the engine fins.